A study of planar inverted-F antennas in a dielectric enclosure

Demand for small and low-profile antennas has greatly increased due to the desire for miniaturisation of modern-day mobile radio electronic terminals. Such an antenna is often integrated into the dielectric casing of a terminal, or independently enclosed within a dielectric radome to provide a protection from operating environments and keep the system more compact. However, the dielectric casing or radome may interact strongly with the antenna and result in losses in performance. The primary focus of this dissertation is to investigate and enhance the performance of Planar Inverted-F Antennas (PIFAs) when enclosed in dielectric casings or radomes for applications in mobile radio communications. PIFAs have attracted much interest due to their small volume, low profile structures and electrical characteristics compatible with existing specifications, making it a promising candidate for mobile radio applications. Therefore, the design of a single band PIFA on a finite ground plane, operating in the 900 MHz band is first presented. It is found that the effect of the finite ground plane must be considered to achieve an optimum performance of the PIFA. Then the performance of this antenna in the presence of a dielectric cover layer is investigated and evaluated in terms of resonant frequency, bandwidth and efficiency. In this study, the dielectric layer represents the dielectric casing of a device where the antenna is much closer to the top part of the casing than to the other side parts whose effect can then be ignored. Computer simulations of performance are based on the Method of Moments (MOM) and have been validated by measurements. This study shows that a dielectric cover layer will strongly interact with the antenna with the result that the antenna performance may move outside the design specifications.Therefore, it is concluded that the dielectric cover layer must always be taken into account in the design stage. In addition, the input and radiation characteristics of a PIFA enclosed within a rectangular dielectric radome for both the 900 MHz and 2400 MHz frequency bands are analysed using the MOM. This research concentrates on the effect of each individual part of the rectangular dielectric radome on the overall performance. It is observed that each individual part has a different degree of effect on both the input and radiation characteristics of the PIFA, and that the effect is more significant at the higher frequency band. The study indicates that the effect of the dielectric radome on the performance of the antenna can be minimised by carefully choosing its location and orientation within the radome. Another indication is that an optimised dielectric radome design can both miniaturise the antenna and at the same time improve the bandwidth without sacrificing other performance parameters such as the gain. Furthermore, an analytical approach based on the Transmission Line Model (TLM) is applied to estimate the input characteristics of a PIFA having a dielectric cover layer. The results calculated based on this approach are compared with MOM computed results. A reasonably good agreement between them has been demonstrated. It is suggested that the TLM model could form part of an efficient Computer Aided Design (CAD) tool for design engineers to provide initial design parameters.Finally, a new dual-band PIFA is proposed. A design example for the Industrial, Scientific and Medical (ISM) frequency bands of 900 MHz and 2400 MHz is given. Measurement validation of the design is presented. The influence of the dielectric cover layer on the resonant frequency, bandwidth, gain and radiation patterns of this antenna is also examined by simulation. In this study, it is found that a simple capacitive disk arrangement not only provides a single feed for dual-band operation but also gives flexibility to allow individual control of the two desired band resonances

Electromagnetic Band Gap Structure Integrated Wearable Monopole Antenna For Spacesuit

Research and development of body-worn communication systems and electronics have become very prominent in recent years. Some applications include intelligent garments equipped with wireless communication devices for sports, astronauts’ spacesuits [1], and fire fighters’ uniforms [2]. These systems are unthinkable without different kinds of body worn textile or flexible antennas. In this thesis, we will discuss the design and fabrication of a compact wearable textile antenna within the Industrial, Scientific and Medical (ISM) band operating frequency, proposed for incorporation into a flight jacket of the astronaut inside the habitat. The antenna is integrated with artificial material known as Electromagnetic Band Gap (EBG) structures for performance enhancement. The purpose of the system is to constantly monitor vital signals of the astronauts. In this thesis the design, simulation, prototype fabrication and antenna testing under different environmental condition, in a word the entire design cycle of wearable Co-Planar Waveguide (CPW) fed monopole antenna is discussed. As human body tissues are lossy in nature, the radiation efficiency of the antenna will be affected due to the absorption of the radiated energy. Therefore, alteration in the radiation characteristics of the wearable antenna like resonant frequency, realized gain and impedance bandwidth will take place. For overcoming these obstacles, addition of EBG layers are recommended to isolate the antenna from near body environments. The proposed wearable antenna was tested under real operating conditions such as pressure and stretching conditions

Factors influencing behavioral intention to use m-learning and the mediation role of user satisfaction

The rapid development of mobile technologies has resulted in a phenomenal growth in the number of youth using the mobile devices for their learning in Malaysia. An understanding on the influence of mobile technologies and its intention to use for learning are crucial. However, there is still a lacking of attention being given by researchers related to this area. Thus, the aim of this study is to investigate the factors influencing intention to use m-learning among students at Malaysian technical universities. The research model has been adopted by combining two related theoretical models, the unified theory of acceptance and use of technology (UTAUT), and the IS success model. A total of 400 sets of data were collected from four Malaysia technical universities using purposeful structured random sampling and self-administrated survey questionnaire. The SPSS AMOS software has been used to test the model of its goodness of fit and the relationships between the variables. The results revealed that the performance expectancy, perceived playfulness, and self-management of learning have a positive significant influence to predict behavioral intention to use m-learning, while social influence and effort expectancy show a negative impact on the behavioral intention. The performance expectancy, self-management of learning and effort expectancy are positively significantly related to user satisfaction while the social influence, and perceived playfulness are negatively significantly related to user satisfaction. It was also found that user satisfaction partially mediates the relationship between performance expectancy and behavioral intention to use m-learning, and the relationship between factors influencing learning and behavioral intention to use m-learning. However, user satisfaction fully mediates the relationship between effort expectancy and behavioral intention to use m-learning

Analysis of an air-spaced patch antenna near 1800 MHz

Microstrip antennas are a type of printed antenna which consists of a patch on top of a grounded substrate. A major limitation for the performance of the patch antenna is the dielectric substrate. The idea of using air as dielectric was therefore considered to overcome that limitation because air has the lowest permittivity and no loss. The goal of this work is to build an air-spaced patch antenna, with the minimum resonant frequency at 1800 MHz and with a return loss of at least 10 dB. This work is novel because the air-spaced patch antenna has not been extensively studied. Existing literature on patch antennas with dielectric were used for the design of the antenna (dimensions of the patch, ground plane and height) and to understand the principles of operation of microstrip patch antennas in general. Simulations using the NEC code and experiments in the RF laboratory were used for this air-spaced patch antenna study. The Numerical Electromagnetic Code (NEC) was used as the simulation tool in this work. The air-spaced patch antenna was simulated to find a trend for the variation of the return loss and impedance with the resonant frequency. Simulation also helped determine cases that will not be meaningful to explore in the experiment. The experiment was done in the RF laboratory of Marquette University College of Engineering. Two procedures were used to calculate the patch dimensions using two different sources ([2], [3]). They lead to two patch antennas that were tested. For each antenna, the height of the dielectric substrate and the recess feed distance were varied. Antenna 2 (procedure 2 – [3]) provided the best results with a resonant frequency of 1800 MHz and a return loss of 21 dB. It was found that the error between experimental and simulation resonant frequency is generally 5% or less. This error increases as the dielectric height increases, and as the recess distance increases. Simulation results roughly follow the experimental results trend

Integration of Antennas and Solar Cells for Autonomous Communication Systems

Solar energy is becoming an attractive alternative for powering autonomous communication systems. These devices often involve the use of separate photovoltaics and antennas, which demand a compromise in the utilization of the limited space available. This thesis deals with the design, analysis, fabrication and validation of different techniques for the integration of antennas and solar cells in a single multifunctional device. Four different photovoltaic technologies are considered within this work, namely, polycrystalline silicon (poly-Si), monocrystalline (mono-Si) emitter-wrap-through (EWT) rear contact solar cells, amorphous silicon (a-Si) thin film on glass substrate, and bifacial solar cells. The use of a poly-Si solar cell was investigated as ground plane for a microstrip patch antenna as well as reflector for a half-wave dipole antenna. Looking forward to further minimize the shade of the solar element on the solar cell and to increase the smart appearance, a film that is both transparent and conductive, the AgHT-4, was evaluated as an antenna radiating element for the integration with an a-Si thin film photovoltaic module on glass substrate. A different approach involves the use of EWT solar cells as a folded dipole for integration with solar concentration. The solar cells in this structure are used both for power generation and as radiating element, and a parabolic trough is employed as well with a double function as solar concentrator for the PV cells as well as reflector for the folded dipole antenna. Numerical simulation results obtained with CST Microwave Studio were validated experimentally with the construction of the corresponding prototypes. The performance of these prototypes is thoroughly evaluated in an anechoic chamber. The approaches proposed in this work for integration of antennas and PV technology will help to reduce the marginal cost of renewable energy, improving its economic viability due to the possibility of an integrated production and easier maintenance. It also reduces the need for cable deployment and leads to compact reliable systems with decreased exposure to natural disasters and vandalism

Impedance Transformers

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